1. Field of the Invention
This invention relates to a three port signal processor capable of real time, wide bandwidth signal convolution and correlation at VHF and lower microwave frequencies. More specifically, this invention relates to a tapped, piezoelectric surface acoustic wave delay line having two ports comprising an interdigital transducer at each end of the delay line separated by an interaction region composed of equi-spaced transducers, each connected to a forward biased semiconductor diode. Nonlinear signal mixing occurs in the diodes, and the signals from the diodes are summed at a third port.
2. Description of the Prior Art
Real time signal correlation and convolution by use of nonlinear wave interaction in VHF and microwave delay lnes is known in the prior art. A nonlinear acoustic wave correlator using nonlinear strain wave propagation in piezoelectric crystals is described in a paper entitled "Convolution and Correlation in Real Time with Nonlinear Acoustics" by C. F. Quate and R. B. Thompson in Applied Physics Letters, No. 16, pp. 494-496 (June 15, 1970). The nonlinearities employed by other investigators include electron-phonon interaction in piezoelectric semiconductor configuration, and magneto-static wave interaction in yttrium-iron-garnet.
Prior art devices as described above, and more specifically the separated medium, semiconductor layer devices, suffer from mechanical fragility, lack of semiconductor uniformity, and high insertion losses.
The nonlinear wave diode correlator described herein overcomes the disadvantages of the prior art devices. By performing signal mixing in a plurality of series or parallel semiconductor diodes located adjacent to the wave interaction region of a piezoelectric, surface acoustic wave delay line, the diode correlator of this invention can perform several different signal processing functions depending on which ports are used for input and output. Insertion loss is considerably reduced from prior art devices. The present diode correlator is a rugged, reliable, completely solid state device with excellent dynamic range characteristics which can be fabricated by standard intergrated circuit technology. Compared with the prior art, it exhibits very long interaction regions and very wide bandwidth. Because the present diode correlator operates with signal inputs of arbitrary amplitude and phase, it performs signal correlation with electronic adaptability. It may be used in radar and communications systems to perform large time-bandwidth pulse compression, electronically variable signal delay, and real time Fourier transformation.